The present invention generally relates to wireless communication networks, and particularly relates to the allocation of Walsh codes to support calls over circuit switched channels.
The Third Generation Partnership Project 2 (3GPP2), a partnership consisting of five telecommunication standards bodies, establishes Code Division Multiple Access (CDMA) standards for wireless communication networks. There are several established CDMA standards, two of which are IS-95 and IS-2000 or cdma2000. Wireless communication networks operable in accordance with IS-95 or IS-2000 Revisions A and B are capable of supporting (a) calls over dedicated channels such as fundamental channels and dedicated control channels and (b) calls over a supplemental channel (hereinafter “SCH”). As used herein, a fundicated channel (“FC”) comprises a fundamental channel, a dedicated control channel, or both fundamental and dedicated control channels. FC calls are typically, but not necessarily, voice calls, and SCH calls are typically data calls having a data rate rarely exceeding 300 kbps. To satisfy the growing demand for high-speed wireless data services at rates beyond 300 kbps, IS-2000 revisions C and D were established and are backward compatible with previous revisions. Revisions C and D are also known as 1xEV-DV, referring to 1 carrier radio transmission technology Evolution for high speed integrated Voice and Data. In accordance therewith, a new channel—a Forward Packet Data Channel (hereinafter “F-PDCH”)—is introduced to support high-speed wireless packet data transmission on the forward link from the network to the mobile station. As apparent from its name, the F-PDCH is a packet switched channel that can be used to support more than one mobile station. That is, the F-PDCH can be shared among a potentially large plurality of packet data users to provide high-speed packet data services to the users sharing such channel.
Because revisions C and D are backward compatible with previous revisions A and B, 1xEV-DV wireless communication networks are capable of supporting (1) traditional voice and data calls established over FCs and SCHs as well as (2) data calls established over a time shared high-speed packet data channel such as the F-PDCH. In practice, FC calls will have higher priority than SCH calls, which in turn will have higher priority than calls over the F-PDCH channel. Therefore, radio resources such as power and Walsh codes will be given to calls based on the following prioritized order: calls established over the FCs; calls established over the SCH and calls established over the F-PDCH(s). Although the SCH does operate in conjunction with the FC, SCH calls or calls over SCH as used herein are defined from the perspective of which channel will the allocated Walsh codes be used for coding. That is, if the network allocates a Walsh code to a call and such allocated Walsh code will be used for coding over a SCH, then such call is defined as a SCH call even though such SCH call also requires the usage of the FCs.
Regarding Walsh coding radio resources, Walsh codes from defined Walsh spaces are first allocated to calls established over the FCs and SCHs. Any leftover or unused Walsh codes can be used to support calls over the F-PDCH. For a given available transmit power, the maximum data rate achievable on the F-PDCH at any given instant depends on the number of Walsh codes available to it. Coding on the F-PDCH uses multiples, not necessarily contiguous, of length-32 Walsh codes from defined Walsh spaces. This coding approach is called multi-code CDMA, and the more codes available for multi-coding F-PDCH transmissions, the higher the achievable data rate.
Theoretically, the Walsh codes used for the F-PDCH can change every 1.25 ms, which is the “slot” timing of the F-PDCH, as the FCs and SCHs occupy more Walsh codes with the arrival of incoming calls or can abandon Walsh codes as current calls over such channels are disconnected from the network. Randomness in that arrival/departure process creates fragmentation in the Walsh spaces resulting in non-contiguous leftover Walsh codes of various lengths in such Walsh spaces. Such fragmentation can reduce the availability of length-32 Walsh codes for assignment to the F-PDCH.